////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8421
SUBJECT: GRB 081028: Swift detection of a burst
DATE: 08/10/28 00:44:50 GMT
FROM: David Palmer at LANL
C. Guidorzi (INAF-OAB), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC),
N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:
At 00:25:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081028 (trigger=332851). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 121.890, +2.311 which is
RA(J2000) = 08h 07m 34s
Dec(J2000) = +02d 18' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). Although this is a BAT image trigger,
the BAT light curve showed at least two slowly rising and falling
peak structure with a duration of about 250 sec. The peak count rate
of the first peak was ~600 counts/sec (15-350 keV), at ~70 sec after the
trigger. The second peak was comparable in size peaking at ~210 sec.
The XRT began observing the field at 00:28:11.5 UT, 190.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 121.8953, +2.3086 which is equivalent to:
RA(J2000) = 08h 07m 34.87s
Dec(J2000) = +02d 18' 30.9"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 20 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 5.50e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of nominal 150 seconds with the White
(160-650 nm) filter starting 200 seconds after the BAT trigger. No afterglow
candidate has been found in the initial data products. Image catalog data are
not available at this time. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.03.
Burst Advocate for this burst is C. Guidorzi (cristiano.guidorzi AT brera.inaf.it).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8424
SUBJECT: GRB 081028: GROND Detection of the Optical/NIR Afterglow Candidate
DATE: 08/10/28 07:44:21 GMT
FROM: Christian Clemens at MPE
C. Clemens, S. Loew and J. Greiner (all MPE Garching) report on behalf of the
GROND team:
We observed the field of GRB 081028 (Swift trigger 332851; Guidorzi et al.,
GCN #8421) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory
(Chile).
Observations started at 06:19 UT on October 28th, 2008, 5.8 hr after the GRB
trigger, and are continuing. They were performed at an average seeing of 1.4"
and at an average airmass of 2.4.
We found a single point source within the 4.8'' Swift-XRT error circle
reported by Guidorzi et al. (GCN #8421) at
RA (J2000.0) = 08h 07m 34.73s
DEC (J2000.0) = +02d 18' 29.1''
with an uncertainty of 0.5".
Based on the first 4.4 min of total exposures in g'r'i'z' and 4.0 min in JHK,
we estimate preliminary magnitudes (all in AB system) of
g' ~ 19.9 mag,
r' ~ 19.3 mag,
i' ~ 19.2 mag,
z' ~ 19.1 mag,
J ~ 19.0 mag,
H ~ 18.7 mag and
K ~ 19.0 mag
with typical errors of +/- 0.1 in g'r'i'z' and +/- 0.15 in JHK. Given
magnitudes are calibrated against SDSS as well as 2MASS field stars.
The object is seen in g' band, implying a redshift smaller than 3.5 and no
statement about variability can be made at this point.
Please note, that no correction for the Galactic foreground extinction
corresponding to a reddening of E_(B-V)= 0.03 mag in the direction of the
burst (Schlegel et al. 1998) has been applied.
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8425
SUBJECT: GRB 081028: optical observations at the NOT
DATE: 08/10/28 07:47:36 GMT
FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst
G. Olofsson (Stockholm), Johan P. U. Fynbo (DARK/NBI), and P. Jakobsson
(Univ. Iceland) report:
We observed the field of GRB 081028 (Guidorzi et al., GCN 8421) with the
NOT equipped with PolCor. Observations started on 2008 Oct 28, around 6
UT (more accurate information will follow).
At a position consistent with the X-ray error circle, we detect a bright
object at the following coordinates:
RA(J2000) = 08:07:34.721
Dec(J2000) = +02:18:29.03
Given the small field of view, only four stars are available for
astrometry. Assuming R = 15.7 for the USNO star at RA=08:07:33.70, Dec =
+02:18:39.9, we compute R ~ 19.2 for the afterglow.
Our astrometry and photometry are consistent with those reported by
Clemens et al. (GCN 8424). The object is not visible in the DSS nor in
the SDSS, hence we are confident it is the afterglow of GRB 081028.
A finding chart is available on request.
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8426
SUBJECT: GRB 081028: TAROT Calern observatory optical observations
DATE: 08/10/28 09:19:04 GMT
FROM: Bruce Gendre at LAM-OAMP
Gendre, B (LAM-OAMP), Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L.
(LATT-OMP) report:
We imaged the field of GRB 081028 detected by SWIFT
(trigger 332851) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.
The observations started 566.4s after the GRB trigger
(423.2s after the notice). The elevation of the field increased
from 16 degrees above horizon and weather conditions
were very poor.
The first useful image started 4054.0 s after the notice. We co-added all
exposure between 4054 and 6499 seconds. At the position reported by Clemens
et al. (GCN 8424) and Olofsson et al. (GCN 8425), we do not detect any
transient source, with a limit of R ~ 17.4. We do not detect any other
source not present in the DSS.
Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.
This message may be cited.
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8427
SUBJECT: GRB 081028: Enhanced Swift-XRT position
DATE: 08/10/28 09:33:20 GMT
FROM: Phil Evans at U of Leicester
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 5305 s of XRT Photon Counting mode data and 8 UVOT
images for GRB 081028, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 121.8948, +2.3083 which is equivalent
to:
RA (J2000): 08h 07m 34.76s
Dec (J2000): +02d 18' 29.8"
with an uncertainty of 1.5 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.
This circular was automatically generated, and is an official product of the
Swift-XRT team.
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8428
SUBJECT: GRB 081028, Swift-BAT refined analysis
DATE: 08/10/28 11:54:31 GMT
FROM: Scott Barthelmy at NASA/GSFC
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), C. Guidorzi (INAF-OAB),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 081028 (trigger #332851)
(Guidorzi, et al., GCN Circ. 8421). The BAT ground-calculated position is
RA, Dec = 121.893, 2.305 deg, which is
RA(J2000) = 08h 07m 34.4s
Dec(J2000) = +02d 18' 16.8"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.
The mask-weighted light curve shows two main peaks and a tail.
The first peak starts at ~T+20 sec, peaks at ~T+80 sec, and falls
to a minumum betwen the two peaks at ~T+140 sec. The second peak
peaks at ~T+220 sec. There is a tail out to approximately T+400 sec.
T90 (15-350 keV) is 260 +- 40 sec (estimated error including systematics).
The time-averaged spectrum from T+29.3 to T+441.5 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.25 +- 0.38,
and Epeak of 58 +- 23 keV (chi squared 57.6 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 3.7 +- 0.2 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+211.74 sec in the 15-150 keV band is
0.5 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index
of 1.84 +- 0.09 (chi squared 63.9 for 57 d.o.f.). All the quoted errors
are at the 90% confidence level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/332851/BA/
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8429
SUBJECT: GRB 081028: Swift-XRT refined analysis
DATE: 08/10/28 12:05:18 GMT
FROM: Cristiano Guidorzi at INAF-OAB
C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) on behalf of the Swift-XRT
team report:
We have analysed the first 6 orbits of Swift-XRT data obtained for GRB
081028 (Guidorzi et al., GCN Circ. 8421), covering 650 s of Windowed
Timing and 12.5 ks of Photon Counting (PC) mode data, between 197 s and
29 ks after the trigger. The UVOT-enhanced XRT position was given by
Evans et al. in GCN Circ. 8427.
The light-curve shows a very complex evolution. In the first orbit data,
covered entirely in WT mode, from 200 to 300 s it can be fit with a
power law decay with an index of ~0.5. This temporally coincides with
the decay of the second peak observed by BAT, which peaked at 220 s
(Barthelmy et al. GCN Circ. 8428). Afterwards, there
is flaring activity up to 400 s. From 400 to 700 s the afterglow
undergoes a steep decay with a power-law index of 3.4, followed by
a large flare with a peak rate of ~30 counts/s and lasting longer
than 150 s. First orbit data stopped during the peak of this flare.
From 4.1 to 8 ks the curve exhibits a steep decay with
a power-law index of 3.8 +- 1.2 and the count rate drops to a value
of ~5e-2 counts/s, after which it experiences a long rebrightening
(at least up to 29 ks) with flaring activity, reaching a peak count
rate of ~0.3 counts/s.
During the first orbit, the WT data spectrum undergoes a significant
hard-to-soft evolution, with Gamma changing from 1 to 3.
A WT spectrum extracted during the steep decay from 400 to 700 s
can be modelled with an absorbed power-law, with Gamma = 2.51 +- 0.07
and NH = (8.0 +- 1.1)e20 cm^-2, in excess of the Galactic column
in this direction of 4.0e20 cm^-2. The observed (unabsorbed) flux
over this time interval is 7.8e-10 (1.1e-9) erg cm^-2 s^-1.
A PC spectrum extracted from 5.0 to 23.2 ks can be modelled with an
absorbed power-law, with Gamma = 2.25 +- 0.16 and
NH = (9.3 +- 3.4)e20 cm^-2. The observed (unabsorbed) flux
over this time interval is 7.3e-12 (1.0e-11) erg cm^-2 s^-1.
Presently, given the ongoing flaring behaviour, we cannot provide a
reliable projection of the count rate over the next hours.
The results of the xrt automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00332851.
This is an official product of the Swift-XRT team.
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8430
SUBJECT: Swift UVOT observations of GRB081028
DATE: 08/10/28 12:41:00 GMT
FROM: Patricia Schady at MSSL/Swift
P. Schady (MSSL-UCL) and C. Guidorzi (INAF-OAB) report on behalf of
the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 081028
201s after the BAT detection (Guidorziet al., GCN Circ. 8421). No
source is detected in any of the individual or coadded exposures in
any of the UVOT filters at the XRT position (GCN Circ. 8427), or at
the position of the reported optical counterpart (GCN Circ. 8424, GCN
Circ. 8425). The 3 sigma upper limits at the position of the optical
counterpart for the first white finding chart (fc) and in consequent
co-added observations are reported below (where T_start and T_stop
represent the elapsed time since the BAT trigger in seconds).
Filter T_start(s) T_stop(s) Exp(s) 3 sigma Upper Limit
white 201 350 146 > 20.95
white 481 846 58 > 20.05
v 357 722 58 > 18.50
b 456 821 58 > 19.33
u 432 796 58 > 18.98
uvw1 407 771 58 >19.01
uvm2 382 746 58 >18.70
uvw2 506 868 55 >19.01
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E(B-V) = 0.03 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383,627).
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8431
SUBJECT: GRB081028: UVOT detection of a brightening afterglow
DATE: 08/10/28 15:40:08 GMT
FROM: Patricia Schady at MSSL/Swift
P. Schady (MSSL-UCL) and C. Guidorzi (INAF-OAB) report on behalf of
the Swift/UVOT team:
Further to the UVOT observations of GRB 081028 reported in GCN Circ.
8430 (Schady et al.), we report an afterglow detection at the position
of the optical counterpart (GCN Circ. 8424, GCN Circ. 8425) in later
UVOT observations, from 10,000s after the BAT trigger. This is
suggestive of a re-brightening of the afterglow consistent with the
time of the brightening observed in the XRT light curve (Guidorzi et
al., GCN Circ. 8429). The afterglow is detected in the v, b and u-band
filters. The detection of the afterglow in the u-filter suggests a
photometric upper limit on the redshift of z < ~2.3.
The magnitudes of the afterglow and 3-sigma upper limits are reported
below:
Filter Tstart(s) Tstop(s) Exp(s) Magnitude/3-sig UL
v 4050 5684 393.2 > 20.13
v 10740 28995 1770.3 20.23 +/- 0.19
b 4870 6504 393.3 > 20.79
b 17436 35567 1433.5 20.19 +/- 0.14
u 4665 6299 393.2 > 20.53
u 16524 34778 2539.8 21.21+/- 0.26
uvw1 4460 6094 393.2 > 20.61
uvw1 15618 33865 2656.7 > 21.89
uvm2 4255 5889 393.2 > 20.51
uvm2 21399 29784 2428.5 > 21.66
uvw2 5281 5480 196.6 > 20.23
uvw2 29001 28082 1771.2 > 20.61
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E(B-V) = 0.03 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383,627).
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8433
SUBJECT: GRB 081028B: Fermi GBM detection
DATE: 08/10/28 21:57:03 GMT
FROM: Elisabetta Bissaldi at MPE
E. Bissaldi (MPE) and A. von Kienlin (MPE)
report on behalf of the Fermi GBM Team:
"At 12:55:08 UT on 28 October 2008, the Fermi GBM triggered
and located GRB 081028B (trigger 246891309 / 081028538).
The on-ground calculated location, using the GBM trigger data,
is RA = 19.8, Dec = -23.5 (J2000 degrees,
equivalent to 1h 19m, -23d 30'), with an uncertainty
of 6.2 degrees (radius, 1-sigma containment, statistical only;
there is additionally a systematic error which is currently
estimated to be 2 to 3 degrees).
The angle from the Fermi LAT boresight is 107 degrees.
This long GRB is single peaked, with an estimated T90 (50-300 keV)
of about 20 s. The time-averaged spectrum (10-1000 keV) from T0-5.1 s to
T0+7.1 s is well fit by a power law function with an exponential
high-energy cutoff. The cutoff energy, parameterized as Epeak,
is 70 +/- 4 keV with a power law index of -0.55 +/- 0.16.
The fluence (10-1000 keV) in this time interval is
(2.0 +/- 0.3)E-06 erg/cm^2. The 1 sec peak photon flux measured starting
from T0+1.5 s in the 10-1000 keV band is 6.9 +/- 0.5 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8434
SUBJECT: GRB 081028: Magellan redshift
DATE: 08/10/28 21:57:17 GMT
FROM: Edo Berger at Harvard
E. Berger, R. Foley (Harvard), R. Simcoe (MIT), and J. Irwin (U. Michigan)
report:
"We observed the optical afterglow (GCNs 8424, 8425, 8430) of GRB 081028
(GCN 8421) with the Magellan Echellette Spectrograph (MagE) on the
Magellan/Clay 6.5-m telescope starting on 2008 Oct. 28.326 UT for a total
integration time of 1800 sec. We find a wide range of absorption features
(including Ly-alpha, SII, NV, SiIV, CIV, FeII, etc.) at a redshift of
z=3.038, which we interpret as the redshift of the GRB. In addition, we
find several intervening CIV and MgII absorbers."
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8442
SUBJECT: GRB 081028: GROND Confirmation of the Optical/NIR Afterglow
DATE: 08/10/29 09:00:11 GMT
FROM: Christian Clemens at MPE
C. Clemens, T. Kruehler and J. Greiner (all MPE Garching) report on behalf of
the GROND team:
We observed the field of GRB 081028 for a second time at 07:45 UT on October
29th, 2008, 31.3 hr after the GRB trigger with 460 s of total exposures in
g'r'i'z' and 480 s in JHK. Observations were performed at an average seeing
of 1.3" and at an average airmass of 1.5.
We still detect the bright afterglow within the refined 1.5'' Swift-XRT error
circle (Evans et al., GCN #8427) with the following preliminary magnitudes
(all in AB system) of
g' ~ 21.26 mag,
r' ~ 20.49 mag,
i' ~ 20.24 mag,
z' ~ 19.99 mag and
J ~ 19.6 mag
with statistical errors of +/- 0.05 in g'r'i'z' and +/- 0.1 in J. Given
magnitudes are calibrated against SDSS as well as 2MASS field stars.
These measurements demonstrate a strong fading of the source compared to our
first epoch observations (Clemens et al., GCN #8424). We therefore confirm
this to be the afterglow of GRB 081028.
No correction for the Galactic foreground extinction corresponding to a
reddening of E_(B-V)= 0.03 mag in the direction of the burst (Schlegel et al.
1998) has been applied.
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8455
SUBJECT: GRB 081028: CrAO optical observations
DATE: 08/11/01 03:04:41 GMT
FROM: Alexei Pozanenko at IKI, Moscow
V. Rumyantsev, V. Biryukov (CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:
We observed the error box of Swift GRB 081028 (Guidorzi et al., GCN 8421)
in R and I bands on Oct. 28, and BVRI on Oct. 29-31 with Shajn telescope of
CrAO. The observations started on Oct. 28 00:40:56 (UT), i.e. ~16 minutes
after burst onset. We clearly detect the afterglow (Clemens et al., GCN
8424, Olofsson et al., GCN 8425) in initial images. Preliminary photometry
of combined images of Oct. 28 based on USNO-B1.0 0923-0196037 star RA
(J2000) = 08:07:36.55, Dec. (J2000) = +02:18:29.4, and assuming R2=15.89
I=15.45 is following:
T0+ Filter, Exposure, mag., err.
(d) (s)
0.0206 R 23x60 21.62 +/- 0.07
0.0415 I 30x60 21.32 +/- 0.09
0.0640 I 30x60 21.43 +/- 0.09
0.0865 I 30x60 21.20 +/- 0.08
0.1091 I 30x60 20.66 +/- 0.05
Our photometry confirms re-brightening of the optical afterglow (Schady &
Guidorzi, GCN 8431) with sharp rise and maximum after ~9400 s which is
consistent with the time of the brightening observed in the XRT light curve
(Guidorzi et al., GCN 8429).
A finding chart of initial combined image in R can be found at
http://grb.rssi.ru/GRB081028/
////////////////////////////////////////////////////////////////////////
TITLE: GCN CIRCULAR
NUMBER: 8499
SUBJECT: GRB 081028 - PAIRITEL NIR detection
DATE: 08/11/08 23:10:09 GMT
FROM: Adam Miller at UC Berkeley
A. A. Miller, B. E. Cobb, J. S. Bloom, D. A. Perley (UC Berkeley), D.
Starr (UCB, LCOGT) report:
We observed the optical afterglow of GRB 081028 (Clemens et al., GCN
8424, Olofsson et al., GCN 8425) with the 1.3-m Peters Automated Infrared
Imaging Telescope (PAIRITEL). Observations with PAIRITEL began at 11:26:23
UT on Oct 28, 2008, 11 hours after the GRB trigger. We detect the
afterglow in a 3727 sec mosaic of 7.8 sec simultaneous exposures in the
J, H, and Ks filters. Preliminary photometry for the afterglow in these
mosaics with midtime 12:13:59 Oct 28, 2008 UT yields J = 17.7 +- 0.1, H =
17.0 +- 0.1, and Ks = 16.1 +- 0.1 (all magnitudes given in the Vega
system), calibrated to the 2MASS system. In intermediate mosiacs we find
that the afterglow gets brighter during our ~1.5 hrs of observations. No
correction for Galactic extinction (E(B-V) = 0.03; Schlegel et al. 1998)
has been made to the above reported values.
These measurements indicate that the burst afterglow became
brighter and redder following the measurements made by Clemens et al.
(GCN 8424). Schady & Guidorzy (GCN 8431) report an optical brightening of
the afterglow, consistent with the detected behavior in the NIR, around
the time of our observations, and further measurements by Clemens et al.
(GCN 8442) taken roughly 31 hours after the burst trigger show that the
afterglow is redder than their initial observations.